Increasing and controlling sensitivity of non-linear metallic thin-film resists

Abstract

Non-linear metallic thermal resist structure having more than two layers of different metals and effective eutectic temperature that is lower than eutectic temperature of a reference non-linear metallic thermal resist having only two layer of same different metals. Optionally, at least one the layers of such resist structure is doped with material different from host metals and/or deposited under conditions resulting in strain or stress in a layer at hand. Method of multi-exposure-based patterning of a substrate carrying such structure with laser pulses characterized by irradiance at levels equal to or below 10 mJ/cm 2 . The sequence of steps producing the required pattern on the substrate may be explicitly lacking a step of removal of a portion of the resist structure between two consecutive exposures.

What is claimed is: 
     
       1. A method for patterning a non-linear metallic thermal resist, the method comprising:
 identifying a first threshold level of exposure, to incident radiation, of a reference structure of a first two-layer stack of respective different first and second metallic materials on a first substrate
 wherein a total thickness of the reference structure is defined by a sum of thicknesses of the first and second reference thin-film layers; 
 and 
 wherein the first threshold level of exposure is a threshold level of exposure required to form an alloy of said first and second materials in said reference structure; 
 
 forming a second thin-film stack on a second substrate, the second thin-film stack (i) containing at least N=3 alternating layers of said different first and second materials, (ii) having a second threshold level of exposure to the incident radiation that is more than ten times lower than the first threshold level of exposure while, at the same time, and (iii) having an overall thickness that is equal to the total thickness, by employing at least one of:
 depositing one or more of said at least N alternating layers at a temperature that is different from a temperature at which another of said at least N alternating layers is deposited to induce a change in a lattice constant of said one or more of said at least N layers; 
 introducing an intermediate layer between two of said at least N alternating layers, said intermediate layer having a lattice constant different from lattice constants of any of the first and second materials; 
 adding, into one or more of said at least N layers, metallic or semiconductor species not present in the first and second materials during a process of deposition of the one or more of said N layers; and 
 implanting material species, not present in the first and second materials, into said second thin-film stack after the second thin-film stack has been deposited; 
 
 
       wherein the second threshold level of exposure is a threshold level of exposure required to form an alloy of said first and second materials in said second thin-film stack;
 projecting a first pre-determined spatial distribution of said incident radiation on the second thin-film stack to cause formation of the alloy of the first and second materials in first areas of said second thin-film stack heated by said incident radiation above a eutectic temperature corresponding to the second threshold level of exposure that is insufficient to cause formation of alloy of the first and second materials in the first two-layer stack. 
 
     
     
       2. A method according to  claim 1 , further comprising additionally projecting a second pre-determined spatial distribution of said light on the target thin-film stack to cause formation of alloy of the first and second materials in second areas of said second thin-film stack heated by said light above the eutectic temperature. 
     
     
       3. A method according to  claim 2 , wherein a thickness of each constituent thin-film layer of said second thin-film stack is less than 5 nm, and wherein any of said projecting and additionally projecting includes exposing said second thin-film stack to pulsed laser light with irradiance less than 2.3 mJ/cm 2  and causes formation of said alloy. 
     
     
       4. A method according to  claim 2 , that is devoid of a step of removing at least a portion of said second thin-film stack between a step of said projecting and a step of additionally projecting. 
     
     
       5. A method according to  claim 1 ,
 wherein said first and second materials include In and Bi, respectively, 
 wherein as a result of said forming, the second thin-film stack is characterized by a curve that represents a rate of absorbance of said incident radiation as a function of depth of the second thin-film stack; 
 wherein the depth of the second thin-film stack is measured from a surface of the second thin-film stack on which said radiation is incident; 
 and wherein said curve has a positive slope in each segment thereof representing absorption of said incident radiation in a corresponding one of said at least N alternative layers. 
 
     
     
       6. A method according to  claim 1 ,
 wherein said first and second materials include In and Bi, respectively, 
 wherein the first two-layer stack is characterized by a curve that represents a rate of absorbance of said incident radiation as a function of depth of the first two-layer stack; 
 wherein the depth of the first two-layer stack is measured from a surface of the first two-layer stack exposed to said incident radiation; 
 and 
 wherein said curve has a negative slope in at least one segment thereof representing absorption of said incident radiation in at least one of layers of the first two-layer stack. 
 
     
     
       7. A method according to  claim 1 , wherein any of said adding and said implanting causes building stress or strain in at least one of constituent thin-film layers of the second thin-film stack during said forming. 
     
     
       8. A method according to  claim 1 ,
 wherein said first and second materials include In and Bi, respectively, and wherein at least one of the following is satisfied: 
 said introducing an intermediate layer includes introducing a layer of In x Bi 1-x , and 
 said adding includes adding any of Pb, Sn, Ga, Si, Ge, Hg, Zr, Ti to form a defects, one or more of said at least N layers, that contain a gaseous element. 
 
     
     
       9. A method for reducing an energy flux of radiation required to form a multi-metallic alloy as a result of exposure of an area of a non-linear multi-metallic thermal resist (NLMTR) to said radiation, the NLMTR having a first overall thickness defined by a sum of thicknesses of two constituent thin-film metallic layers thereof, said constituent thin-film metallic layers being made of two different materials, the method comprising:
 altering a design of a structure of composed of two constituent thin metallic layers NLMTR to increase a number of constituent thin-film metallic layers thereof and to define a thin-film stack that has a bigger number of thin-film layer interfaces than that in the NLMTR while having a second overall thickness equal to the first overall thickness, the second overall thickness defined by a sum of thicknesses of constituent thin-film metallic layers of said thin-film stack; 
 and 
 sequentially depositing constituent thin-film layers of said thin-film stack on a substrate to form a target nonlinear multi-metallic thermal resist that is characterized by 
 (a) having the two different materials, and 
 (b) an altered energy flux of radiation required to form a multi-metal alloy as a result of exposure of an area of said thin-film stack to said radiation, the altered energy flux being more than ten times smaller than the energy flux required to form a multi-metallic alloy as a result of exposure of the NLMTR to said radiation, 
 wherein said sequentially depositing includes at least one of 
 i) depositing the constituent thin-film layers at different temperatures to modify a lattice constant of at least one of said constituent layers; 
 ii) forming dopant sites in at least one of said constituent thin-film layers of the target thin-film stack with material species absent from the two different materials; 
 iii) introducing an intermediate layer between first and second of said constituent thin-film layers of the target thin-film stack, said intermediate layer having an atomic spacing that differs from an atomic spacing of any of said constituent thin-film layers; and 
 iv) implanting material species, absent in the first and second materials, into said second thin-film stack after the second thin-film stack has been deposited. 
 
     
     
       10. A method according to  claim 9 ,
 wherein said two different materials include In and Bi, respectively, 
 wherein as a result of said sequentially depositing, the thin-film stack is characterized by a curve that represents a rate of absorbance of said radiation as a function of depth of the thin-film stack; 
 wherein the depth of the thin-film stack is measured from a surface of the thin-film stack exposed to said radiation; 
 and wherein said curve has a positive slope in each segment thereof representing absorption of said radiation in a corresponding one of the constituent thin-film layers. 
 
     
     
       11. A method according to  claim 9 , wherein said sequentially depositing includes depositing at least one metallic thin-film layer structured as a lattice, wherein thicknesses of each of the constituent thin-film layers of said thin-film stack is less than 5 nm. 
     
     
       12. A method for patterning a non-linear metallic thermal resist, the method comprising:
 forming, on an underlying substrate, a stack of materials including the resist that has a first overall thickness and three or more alternating thin-film layers of two different metallic materials such that a first threshold level of exposure, of the resist to incident radiation, required to form an alloy of the different metallic materials is more than ten times lower than a corresponding second threshold level of exposure of a reference non-linear metallic thermal resist to the incident radiation, 
 depositing, on the resist, a barrier layer configured to protect the different metallic materials from erosion by an immersion fluid, 
 projecting, through the immersion fluid, a first pre-determined spatial distribution of light on the stack such as to cause formation of alloy of the different metallic materials of the stack in first areas of said resist heated above a corresponding eutectic temperature, 
 wherein said reference non-linear metallic thermal resist has a second overall thickness and structured to have only two thin-film layers of the same different metallic materials, the first and second overall thicknesses being equal, 
 wherein said forming includes at least one of 
 i) depositing sequential layers of said three or more thin-film layers at different temperatures; 
 ii) forming dopant sites in at least one of said three or more thin-film layers, said dopant sites containing materials not present in said two different metallic materials; and 
 iii) introducing an intermediate layer between said three or more thin-film layers, a first of the three or more thin-film values having a first atomic spacing, a second of the three or more thin-film values having a second atomic spacing, the intermediate layer formed from a material with a third atomic spacing, the third atomic spacing being greater than the first atomic spacing and smaller than the second atomic spacing. 
 
     
     
       13. A method according to  claim 12 , further comprising additionally projecting a second pre-determined spatial distribution of light on the stack to cause formation of alloy of said different metallic materials in second areas of said resist heated above a corresponding eutectic temperature. 
     
     
       14. A method according to  claim 13 , wherein any of said projecting and additionally projecting includes exposing said stack to pulsed laser light with irradiance equal to or less than 10 mJ/cm 2 . 
     
     
       15. A method according to  claim 12  that is devoid of a step of removing at least a portion of said stack between steps of said projecting and said additionally projecting. 
     
     
       16. A method according to  claim 12 , further comprising depositing said resist on the underlying substrate such as to form a multi-layered metallic film at least one layer of which is configured as a lattice. 
     
     
       17. A method according to  claim 12 , further comprising doping at least one of said different metallic materials. 
     
     
       18. A method according to  claim 12 ,
 wherein said two different metallic materials include In and Bi, 
 wherein as a result of said forming, the resist is characterized by a curve that represents a rate of absorbance of said incident radiation as a function of depth of the resist; 
 wherein the depth of the resist is measured from a surface of the resist on which said radiation is incident; 
 and 
 wherein said curve has a positive slope in each segment thereof representing absorption of said incident radiation in a corresponding one of said three or more alternating thin-film layers.